Nutritional and Microbiological Evaluation of Fermented Cereal Weaning Foods

Sammanfattning: Protein energy malnutrition (PEM) is the most serious nutritional problem affecting pre-school children in developing countries. The low energy and nutrient density of the diet and the presence of anti-nutritional factors contribute to this condition, as do the low frequency of feeding and transmission of diarrhoea-causing pathogens via the food.

The overall objective of this thesis was to evaluate the use of lactic acid fermentation in order to improve the nutritional quality and microbiological safety of cereal weaning foods. The study focused on Tanzanian cereal staple foods, and the nutritional factors specifically studied included dietary bulk properties, in vitro protein digestibility and in vitro estimation of iron availability. The microbiological study evaluated the survival of diarrhoea-causing pathogens in lactic acid-fermented gruels. A prospective epidemiological study was carried out to evaluate the effect of regular consumption of lactic acid-fermented gruels on the diarrhoea prevalence in pre-school children living in a rural setting of Tanzania.

With a fermentation technique using a natural lactic acid starter culture and addition of flour of germinated seeds, it was possible to prepare liquid cereal gruels from maize, white sorghum, bulrush millet and finger millet with a 30 to 35% flour concentration. The energy density of such a lactic acid-fermented gruel was about 1.2 kcal/g, as compared with 0.4 kcal/g in a non-fermented gruel prepared to the same consistency. This represents a threefold increase in energy density. Fermentation of high-tannin sorghum gruels only resulted in a double increase of the energy density while maintaining a liquid consistency.

The in vitro protein digestibility of high-tannin cereal varieties was significantly (p<0.01) increased from a range of 32 to 40% before fermentation to a range of 41 to 60% after lactic acid fermentation. Non-tannin cereal varieties had in vitro protein digestibility values in the range of 61 to 79% before fermentation and slightly increased values in the range of 70 to 88% after lactic acid fermentation.

Lactic acid fermentation of non-tannin cereals with added fluor of germinated sorghum grain or wheat phytase increased the iron solubility from about 4% to 9% and 50%, respectively. Soaking the flour in water before fermentation had a similar effect as addition of wheat phytase. The increase in soluble iron was strongly related to enzymatic degradation of phytate (p<0.001). The fermentation process itself also seemed to improve the iron solubility. High-tannin cereals showed a minor increase in soluble iron after fermentation, which is ascribed to the inhibitory effect of tannins, both on the iron solubility per se and on the enzymatic hydrolysis of phytate.

Lactic acid-fermented gruels inhibited the proliferation of inoculated Gram-negative pathogenic bacteria, such as enterotoxigenic Escherichia coli, Campylobacter jejuni, Shigella flexneri and Salmonella typhimurium as well as Gram-positive bacteria. The mean number of diarrhoea episodes in a group of pre-school children over a 9-month period was 2.1 per child using fermented gruels, compared with 3.5 per child using non-fermented gruels (p<0.001).